Blade cutting edges used in machinery, hand tools and shaving devices have a common problem of maintaining a sharp edge. This problem comprises corrosion damage caused by harsh environmental working conditions. Blade cutting edge corrosion occurs when free electrons from the metal cutting edge flow across a boundary into a contacting layer of moisture. Blade cutting edges comprise metal material conductors with large numbers of these free electrons. Free electrons comprise mobile electrons and are not to be confused with planetary electrons. Planetary electrons are held within the atom by strong electrostatic forces while free electrons move randomly within the conductor. This random movement causes collisions with atoms that is how electrical energy is transmitted through a metallic conductor causing corrosion.
Corrosion comprises the electrochemical attack of a metal surface that occurs in the presence of water and oxygen. Blade cutting edge corrosion comprises wet corrosion that begins in the form of rusting. Rusting occurs when aqueous solutions are allowed to remain on unprotected areas of a blade cutting edge surface. Blades comprise sharp cutting edges and free electrons accumulate along these sharp edges. Different parts of the cutting edge surface accumulate more electrons than others and act like electrodes. This electrode like action begins to release free electrons from the cutting edge thereby forming metallic ions. These metallic ions are then absorbed by ions in the electrolyte water solution. This metallic ion absorption by ions in the electrolyte solution causes the dissolution of the metal cutting edge. Dissolution comprises the taking up of a substance by a liquid. This dissolution process begins at the free electron discharge points. The process of dissolution causes small metal particles to break off the blades fine cutting edge forming pits. Loss of these small particles allows the electrolyte water solution to penetrate the metal cutting edge and increases the rate of dissolution. This dissolution causes a condition known as accelerated pitting. As the pitting increases, larger particles begin to break off the fine cutting edge causing corrosion pitting damage. This corrosion pitting damage changes the blade's sharp cutting edge into a jagged irregular dull edge surface. This corrosion pitting damage is one of the most difficult types of corrosion to prevent.
The problem of corrosion rusting and pitting has changed the way blade cutting edges are manufactured. The long utilized high carbon steels used in the manufacturing of blade cutting edges are easily damaged by corrosion. To find a corrosion free blade cutting edge material, corrosion resistant stainless steel alloy blades were developed. Stainless steel alloys, while somewhat resistant to corrosion, do not maintain as sharp a blade cutting edge as high carbon steels. Carbide tip blade cutting edges advanced the fight against corrosion damage; however, unlike stainless steel and carbon steel, carbide tip blades are costly, brittle and require specialized equipment to sharpen the cutting edge. This prevents carbide tip blades from being sharpened in the field which is a significant problem. Cutting tools used in forestry operations, lumber mills and remote locations use carbon steel blade cutting edges due to their economical price and ease of on-site sharpening.
Another advance in the fight against blade cutting edge corrosion was the development of specialized coatings. Blade cutting edges often have sprayed on protective metal films and plastic coatings to prevent corrosion damage; however, these films and coatings are destroyed during the first use of the blade cutting edges. This destruction of the protective coating leaves the blade cutting edges open to electrochemical corrosion attack in the form rusting and pitting damage.